1070-4272/04/7709-1460C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 9, 2004, pp. 1460!1468. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9,
2004, pp. 1472!1480.
Original Russian Text Copyright + 2004 by Lukiyanchuk, Rudnev, Kuryavyi, Gordienko.
AND CORROSION PROTECTION OF METALS
Anodic-Spark Layers on Aluminum and Titanium Alloys
in Electrolytes with Sodium Phosphotungstate
I. V. Lukiyanchuk, V. S. Rudnev, V. G. Kuryavyi, and P. S. Gordienko
Institute of Chemistry, Far Eastern Division, Russian Academy of Sciences, Vladivostok, Russia
Received June 16, 2003; in final form, January 2004
Abstract-The influence exerted by the pH of an aqueous 0.0083 M solution of Na
] on the
composition and morphology of anodic coatings galvanostatically formed on aluminum and titanium alloys
at sparking and breakdown voltages was studied.
Anodic treatment of rectifying metals in aqueous
electrolytes in the sparking and microarc mode (hence-
forth, anodic-spark deposition) can give coatings that
contain, in addition to oxides of a metal or alloy being
treated, oxygen compounds of elements contained in
the electrolyte. As a result, coatings that exhibit func-
tions typical of anodic films and are promising for use
in catalysis , as active elements of gas analyzers
[2, 3], and bioinert compounds  can be obtained.
As an example can serve the formation on titanium of
layers that contain barium, strontium, or lead titanates
and exhibit ferroelectric properties [5, 6].
One of the main processes that determine the com-
position of the forming anodic-spark layers is ther-
molysis of the electrolytic deposit around electric-
breakdown channels. Use of electrolytes containing
anionic complexes opens up additional opportunities
for directed formation of oxide structures. Coatings of
various compositions and purposes can be obtained in
electrolytes of this kind. For example, wear-resistant
coatings containing a-Al
are obtained in solutions
with hexafluoroaluminate complexes ; corrosion-
resistant coatings with vanadium oxides, in electro-
lytes with phosphovanadate heteropolyanions [8, 9];
biocidal coatings with zinc phosphates, in solutions
with zinc polyphosphate complexes ; bioinert
coatings with hydrooxyapatite for implants, in elec-
trolytes with calcium glycerophosphate complexes ;
and light-reflecting coatings that contain ZrO
resistant to the action of hard ultraviolet, in solutions
with alkali metal hexafluorozirconate complexes .
At the same time, the processes of coating forma-
tion in electrolytes with anionic complexes are now in
the stage of research and accumulation of experi-
mental data. Among such electrolytes, those contain-
ing iso- and heteropolyanions (IPA and HPA) are the
least studied. The interest in these electrolytes is
due to the following.
(a) The variety of IPA and HPA is rather wide.
Only the position of the central atom in an HPA can
be occupied by more than 60 elements . Forma-
tion of coatings with diverse chemical compositions
would be expected in electrolytes with HPA. These
compositions must, apparently, reflect the scheme of
thermal transformations of HPA or of products formed
in their interaction with a metal being anodized.
(b) Conditions for formation of IPA and HPA are
satisfied in many aqueous solutions that are used in
anodic-spark oxidation and contain compounds of
vanadium, molybdenum, and tungsten in higher oxi-
dation states. Consequently, revealing the relationship
between the presence or absence of HPA in electro-
lytes and the composition of the anodic-spark layers
being formed is both practically and theoretically
(c) Thermal decomposition of heteropoly com-
pounds is used to produce oxide catalysts . It is
quite possible that thermolysis of HPA or products of
their interaction with a metal being anodized, which
occurs near electric-breakdown channels, will make it
possible to form on metals oxide structures promising
as regards their possible catalytic activity.
(d) It has been shown previously that films formed
in electrolytes with HPA show satisfactory protective
properties [8, 14, 15].
Until now, fundamental aspects of how the ele-
ments contained in HPA are incorporated into coat-
ings on rectifying metals have been studied in multi-
component electrolytes containing simultaneously